const Koa = require('koa');
const app = new Koa();
app.use((ctx, next) => {
    console.log('第一层中间件');
    next();
    console.log('第一层中间件.. ...');
})
app.use((ctx, next) => {
    console.log('第二层中间件');
    next();
    console.log('第二层中间件.. ...');
})
app.use((ctx, next) => {
    console.log('第三层中间件');
})
app.listen(3000);